Lastly, plug in the three runs of LED power cables.
We suggest cutting out the yellow wires so you don't accidentally connect to the 12V lines.
Don't do your testing in a rush! Be careful and methodical!
Once everything is powered on, your computer should detect an external display. Adafruit receiver/senders are pre-programmed so you should see some video depending on your monitor configuration. If you can 'mirror' your display that is easiest to debug.
If you have a different setup than this tutorial, don't worry if the LED wall is acting funny or not on at all. This will be fixed in the next step. As long as the green lights are flashing on both the sender and receiver cards then that means that data is being transmitted.